Procedure Qualification (WPS/PQR)
Procedure Qualification (WPS/PQR)
A welding procedure specification (WPS) is a written document that provides direction to the welder for making production welds. It must be supported by a procedure qualification record (PQR), which documents the actual welding parameters and test results used to qualify the procedure. In Canada, CSA W47.1 and CSA W59 govern the qualification of welding procedures for steel structures. Key concepts include essential variables, nonessential variables, and supplementary essential variables. Essential variables (e.g., base metal thickness, filler metal classification, preheat temperature) must be within the ranges qualified by the PQR. Nonessential variables (e.g., joint design details) can be changed without requalification. Supplementary essential variables (e.g., impact testing requirements) apply only when toughness is specified.
A common trap is assuming that a PQR qualified on one base metal can be used for another without checking the material grouping. For example, PQRs qualified on Group 1 steels may not cover Group 2 steels unless specifically tested. Another trap is forgetting that a WPS must be available at the work site and followed exactly. Also, the PQR must record actual test results, not just the parameters.
Worked example: A PQR was qualified using E4918 (E7018) electrode on 10 mm thick steel with a preheat of 100°C. The WPS covers thickness from 5 mm to 20 mm and preheat from 100°C to 150°C. If a production weld requires 25 mm thickness, the WPS does not cover it; a new PQR is needed. If the production weld uses E4918 but with preheat of 80°C, that is below the qualified minimum, so it is not permitted.
Rule of thumb: Always compare the proposed welding parameters against the essential variables listed in the PQR. If any essential variable falls outside the qualified range, requalification is required.